Object detection systems for determining range and velocity of a target object are also known as radar systems (radio detection and ranging). Frequency modulated continuous wave (FMCW) object detection or radar systems use a transmission signal with linearly increasing frequency. FMCW systems permit to obtain range and velocity of a target object simultaneously. Range can be obtained with the detection of the frequency shift between the transmission signal and the reception signal. Velocity can be obtained by detecting the Doppler shift. When using higher frequency signals, the Doppler shift increases, but also the maximum unambiguously detectable velocity (speed) decreases.
U.S. Pat. No. 6,606,052 B1 discloses a method and an apparatus for multiple object detection by automotive FMCW radars providing distance and relative velocity information. A two chirp frequency sweep with small slope difference is utilized and, since the difference is small, the distance information can be obtained by automatically eliminating the Doppler frequency.
US 2010/0289692 A1 discloses a radar system and method using an electromagnetic wave having a period comprising a number of consecutive ramps. A first ramp in the period is transmitted over a first portion of a frequency range, and a second ramp in the period is transmitted over a second portion of the frequency range that differs from the first portion. The second ramp is offset by a frequency shift relative to the first ramp.